WORKPLACE, EQUIPMENT, AND TOOL DESIGN

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WORKPLACE, EQUIPMENT, AND TOOL DESIGN

• IENG 301
• FUNDAMENTALS OF
• WORK STUDY AND
• ERGONOMICS

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Ergonomics

• Designing the workplace, tools, equipment and
  work environment to fit the human operator is
  called ergonomics.

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Principles of Work Design

• Increased production and efficiency of the
  operation,
• Decreased injury rates for the human operator.

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Anthropometry and Design

• The primary guideline is to design the workplace
  to accomodate most individuals with regard to
  structural size of the human body
• The science of measuring the human body is termed
  anthropometry.

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Design

• Designing for most individuals is an approach
  that involves the use of one of three different
  specific design principles, as determined by the
  type of design problem.
• Design for Extremes
• Design for Adjustability
• Design for the Average

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Design fo Extremes

• Implies that a specific desing feature is a
  limiting factor in determining either the maximum
  or minimum value of population variable that will
  be accomodated.
• e.g. Clearances, such as doorway or opening into
  a storage tank should be designed for the maximum
  individual, that is, a 95 percent of all males
  and almost all females will be able to enter the
  opening.
• Added space in military aircraft or submarines
  is expensive, therefore designed to accomodate
  only a certain (smaller) range of individuals.

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Design for Adjustability

• is typically used for equipment or facilities
  that can be adjusted rto fit a wider range of
  individuals.
• e.g. Chairs, tables, desks, vehicle seats,
  steering columns, and tool supports
• (ranging from 5th percentile females to 95th
  percentile males)
• It is the preferred method of design, but there
  is a trade-off with the cost implementation.

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Design for the Average

• is the cheapest but least preferred approach.
• Eventhough there is no individual with all
  average dimensions, there are certain situations
  where it would be impractical ot roo costly to
  include adjustability for all features.
• e.g. Most industrial machine tools are too large
  and too heavy to include height adjustability for
  the operator.
• Designing operating height at the 50th percentile
  of the elbow height for the combined female and
  male populations means that most individuals will
  not be excessively inconvinienced.

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Seating design in a large training room
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Principles of Work Design The Workplace

• Determine the work surface height by elbow height
• The work surface height (seated/standing) should
  be determined by a comfortable working posture
  for the operator.
• This means that the upper arms are hanging down
  naturally and the elbows are flexed at 90 degrees
  so that the forearms are parallel to teh ground.

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Principles of Work Design The Workplace

• Adjust the work surface height based on the task
  being performed
• For rough assembly involving the lifting of heavy
  parts, it is more advantageous to lower the work
  surface by 20 cm to take the advantage of the
  stronger trunk muscles,
• For fine assmebly involving minute visual
  details, it is more advantageous to raise the
  work surface up to 20 cm to bring the details
  closer to the optimum line of sight of 15
  degrees,
• Another, perhaps better, alternative is to slunt
  the work surface approximately 15 degrees to
  satisfy both principles.

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Principles of Work Design The Workplace

• Adjust the work surface height based on the task
  being performed
• These principles also apply to a seated
  workstation.
• A majority of tasks, such as writing or light
  assembly are best performed at the resting-elbow
  height.
• Seated workstations should be provided with
  adjustable chairs and adjustable footrests.

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Principles of Work Design The Workplace

• Provide a comfortable chair for the seated
  oeprator
• It is very important to privde lumbar support in
  the form of an outward bulge in the seat back, or
  even a simple lumbar pad placed at the belt level

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Principles of Work Design The Workplace

• Provide adjustability in the seat
• A second cinsideration is the reduction of disk
  pressure, which can increase considerably with a
  forward tilt of the trunk.
• Seat height is most critical, with ideal heihgt
  being determined by the persons popliteal
  height.
• Armrests for shoulder and arm support and
  footrests for shorter individuals are recommended.

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Principles of Work Design The Workplace

• Encourage postural flexibility
• The workstation height should be adjustable so
  that work can be performed efficiently either
  standing or sitting.
• Provide antifatigue mats for a standing operator
• Standing for extended periods of time on a cement
  floor is fatiguing.
• The mats allow smal muscle contractions in the
  legs, forcing the blood to move and keeping it
  from tending to pool in the lower extremities.

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Principles of Work Design The Workplace

• Locate all tools and materials within the normal
  working area
• The greater the distance, the larger the muscular
  effort, control and time
• Therefore, it is important to minimize the
  distances

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Principles of Work Design The Workplace

• Fix locations for all tools and materials to
  permit the best sequence
• In driving an automobile, the break pedal is in a
  fixed location, no time is required to decide
  where the brake is located.
• Use gravity bins and drop delivery to reduce
  reach and move times
• The time required to perform both of the
  transport therbligs reach and move is
  directly proportional to the distance that the
  hands must move in performing these therbligs.

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Principles of Work Design The Workplace

• Arrange tool, controls, and other components
  optimally to minimize motions
• The most important or most frequently used
  components should be placed in the most
  convinient locations
• e.g. Emergency stop button should be placed in a
  readily visible, reachable, or convinient position

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Principles of Work Design Machines and Equipment

• Take multiple cuts whenever possible by combining
  two or more tools in one, or by arranging
  simultaneous cuts from both feeding devices
• Use a fixture instead of the hand as a holding
  device

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Principles of Work Design Machines and Equipment

• Locate all controldevices for best operator
  accessibility and strength capability
• Handwheels, cranks and levers should be of such a
  size and placed in such positions that operators
  can manipulate them with maximum proficiency and
  minimum fatigue.
• Frequently used controls should be positioned
  between elbow and shoulder height.
• Seated operators can apply maximum force to
  levers located at elbow level, standing
  operators, to levers located at shoulder height

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Principles of Work Design Machines and Equipment

• Use shape, tecture and size coding for controls
• Shape coding, using two or three dimensional
  geometric configurations, permits both tactual
  and visual identification.

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Principles of Work Design Machines and Equipment

• Use proper control size, displacement and
  resistance
• Insure proper compatibility between controls and
  displays

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Cumulative Trauma Disorders (CTD)

• CTD (repetitive motion injuries or work-related
  musculoskeletal diorders) are injuries to the
  musculoskeletal system that develop gradually as
  a result of repeated microtrauma due to poor
  design and the excessive use of hand tools and
  other equipment.

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Cumulative Trauma Disorders (CTD)

• National Safety Council (USA) suggest that 15-20
  of workers in key industries (meatpacking,
  poultry processing, auto assembly, garment
  manufacturing) are at potential risk for CTD.
• 61 of all occupational illnesses are associated
  with repetitive motions.

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Cumulative Trauma Disorders (CTD)

• Four major work-related facors lead to the
  development of CTD
• Excessive force
• Awkward or extreme joint motions
• High repetition
• Duration of work

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Cumulative Trauma Disorders (CTD)

• Tenosynovitis inflammation of the tendon sheaths
  due to overuse or unaccustomed use of improperly
  designed tools
• Tendinitis if the inflamations spreads to the
  tendons
• Carpal Tunnel Syndrome a disorder of the hand
  caused by injury of the median nerve inside the
  wrist

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Principles of Work Design Tools

• Use a power grip for tasks requiring force and
  pinch grips for tasks reqiring precision

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Principles of Work Design Tools

• Avoid prolongeed static muslce loading
• Perform twisting motiins with elbows bent
• Maintain a straight wrist
• Avoid tissue compression

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Principles of Work Design Tools

• Design tools so that they can be used by either
  hanf and by most individuals
• Avoid repetitive finger action
• Use the strongest working fingers the middle
  finger and the thumb

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Principles of Work Design Tools

• Design 1.5 inch handle diameters for power grips
• Design handle lengths to be a minimum of 4 inches
• Design a 3-inch grip span for two-handled tools

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Principles of Work Design Tools

• Design appropriately shaped handles
• Design grip surface to be compressible and
  nonconductive
• Keep the weight of the tool below 5 pounds
• Use gloves judiciously

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Principles of Work Design Tools

• Use power tools such as nut and screwdrivers
  instead of manual tools
• Use the proper configuration and orientation of
  power tools

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Principles of Work Design Tools

• Choose a power tool with the proper
  characteristics
• Use reaction bars and tool balancers for power
  tools